Closed drift ion source

• US 20050247885A1
• Filed: 07/08/2005
• Published: 11/10/2005
• Est. Priority Date: 04/10/2003
• Status: Active Grant

• Current Assignee: General Plasma, Inc. (BASF SE)
• Original Assignee: General Plasma, Inc. (BASF SE)
• Inventors: Madocks, John
• Granted Patent: US 7,259,378 B2
• Time in Patent Office: Days
• US Class Current: 250/423.R
• CPC Class Codes: F03H 1/0075 with an annular channel; Hall-effect thrusters with closed electron drift
• CPC Class Codes: H01J 27/143 Hall-effect ion sources with closed electron drift
• CPC Class Codes: H05H 1/54 Plasma accelerators

Abstract

A closed drift ion source which includes a channel having an open end, a closed end, and an input port for an ionizable gas. A first magnetic pole is disposed on the open end of the channel and extends therefrom in a first direction. A second magnetic pole disposed on the open end of the channel and extends therefrom in a second direction, where the first direction is opposite to the second direction. The distal ends of the first magnetic pole and the second magnetic pole define a gap comprising the opening in the first end. An anode is disposed within the channel. A primary magnetic field line is disposed between the first magnetic pole and the second magnetic pole, where that primary magnetic field line has a mirror field greater than 2.

Claims

1. A closed drift ion source for generating an accelerated ion beam comprising:

a closed loop discharge region into which ionizable gas can be introduced;

an anode located at one longitudinal end of said region, the other end of said region open to allow ion flow out of said discharge region;

a first magnetic pole located radially inward from said region;

a second magnetic pole located radially outward of said region;

a magnetic mirror field in the discharge region wherein said magnetic mirror field is created by said magnetic poles, and wherein said magnetic mirror field comprises a primary magnetic field line between said magnetic poles;

wherein said mirror field is centered on the primary magnetic field line, wherein said magnetic mirror field has a minimum ratio greater than 2.

2. The closed drift ion source of claim 1, wherein said mirror field is substantially symmetric.

3. The closed drift ion source of claim 1, further comprising:

an electric circuit, wherein the first and second magnetic poles serve as the cathode electrode of the electrical circuit.

4. The closed drift ion source of claim 1, wherein the first and second magnetic poles are not part of the electrical circuit and are electrically isolated.

5. The closed drift ion source of claim 1, wherein the magnetic mirror field wherein the weakest magnetic mirror field from one or the other pole structure surface to the central gap region exceeds a ratio of 4.

6. The closed drift ion source of claim 1, wherein said magnetic poles are shaped to magnify said magnetic field, and wherein the magnetic field at the surface of the pole structure at the discharge region exceeds the strength of the magnetic source field.

7. A closed drift ion source for generating an accelerated ion beam comprising:

a closed loop discharge region into which ionizable gas can be introduced;

an anode located at one longitudinal end of said region, the other end of said region open to allow ion flow out of said discharge region;

a first magnetic pole having internal and external pole surfaces, said first magnetic pole located radially inward from said region;

a second magnetic pole having internal and external pole surfaces, said second magnetic pole located radially outward of said region;

wherein said poles are shaped to a point including bevels on both internal and external pole surfaces.

8. The closed drift ion source of claim 7, wherein said pointed pole bevels comprise a stepped structure.

9. The closed drift ion source of claim 7, wherein said pointed pole bevels include curved shapes.

10. The closed drift ion source of claim 7, wherein at least a portion of said anode is located between said beveled poles.

11. A method to focus a plasma, comprising the steps of:

providing an ionizable gas;

introducing said ionizable gas into a closed drift ion source comprising a first magnetic pole and a second magnetic pole separated by a gap;

producing a primary magnetic field line disposed between said first magnetic pole and said second magnetic pole, wherein said primary magnetic field line has a mirror field greater than 2; and

forming in said gap a plasma from said ionizable gas.

12. The method of claim 11, further comprising the step of producing a symmetric primary magnetic field line.